The aim of this study was to investigate the effect of some pesticides (Methomyl, Deltamethrin and Chlorpyrifos), zeolite, silica gel and ferric oxide on the immobilization of some heavy metals (Cd, Ni, Cr and Pb) in sewage sludge. The results indicated that the application of 3 g of Deltamethrin 100g-1 sludge decreased the DTPA- extractable content of Cd, Ni, Cr and Pb by 25, 21, 46 and 16%, respectively. Adding 1.5 ml Chlorpyrifos/100 g sludge caused significant increase in extractable Cd, Ni and Pb by 39, 38 and 16%, respectively, compared with the control treatment.
Application of 15% (w w-1) zeolite to the sludge resulted in the maximum decrease in both extractable Cd (from 0.90 ppm in the control to 0.33 ppm) and Pb (from 26.7 ppm in the control treatment to13.4 ppm). Application of 25% silica gel decreased DTPA extractable Cr by 74%. Application of a mixture of silica gel with zeolite or with ferric oxide completely retained all the extractable Ni.